1. Field of the Invention
This invention relates in general to subsea oil and gas production systems and in particular to a subsea tree assembly having certain components that are retrievable by a light-duty workover vessel.
2. Description of the Prior Art
A conventional subsea wellhead assembly includes a wellhead housing which supports one or more casing hangers located at upper ends of strings of casing extending into the well. A production tree is landed on the wellhead for controlling the production of well fluids. The tree usually carries a choke and valves to control the flow and sensors to monitor the flow.
With both conventional and horizontal trees, external chokes and production valves are used to control the flow. If the valves or choke are in need of service, retrieval is difficult and may require the use of a remotely-operated vehicle. Various valves and controls have been located on an apparatus separately retrievable from the tree, but many of the components requiring service may require that the entire tree be removed.
A subsea well apparatus is provided for controlling and monitoring production fluid flow from a well. A christmas tree is adapted to land on a subsea wellhead, the tree having a tubular, open upper end. A first flow passage extends from a lower end of the tree to the upper end for communicating fluid with the well. A second flow passage extends downward from the upper end of the tree and has an outlet on a sidewall of the tree for communicating with a flowline. The second flow passage is connected to an annulus access passage and is separated from the annulus access passage by a valve. A production module lands on and is retrievable from the upper end of the tree, the module having a flow loop with one end in communication with the first flow passage and another end in communication with the second flow passage. At least one flow interface device is located in the loop of the production module. The flow interface device may be used to monitor or control the flow and may be a temperature or pressure sensor, a flow or multi-phase flow meter, or a choke.